The present invention relates to an image forming apparatus comprising a plurality of light beam sources and photoreceptors corresponding to each of the light beam sources, which forms images corresponding to electrostatic latent images formed on a surface of each photoreceptor on a recording medium in an overlaid state by exposure to plural light beams.
The image forming apparatus such as a laser printer, particularly a color image forming apparatus comprises a plurality of light beam sources, photoreceptors corresponding to each of the light beam sources, a deflecting part for deflecting light beams generated by each light beam source, mirror for guiding the light beams thus scanned to each photoreceptor corresponding to the light beam source, and at least one lens for imaging the light beams guided by the mirror on the surface of each photoreceptor. The image forming apparatus forms a color image by forming an electrostatic latent image on the surface of each photoreceptor by exposure to the light beams, developing the electrostatic latent image thus formed by sticking different colors of toner on the electrostatic latent image, transferring toner images thus formed on the photoreceptors to the recording medium so that the toner of different colors carried by the photoreceptors are transferred to a medium to be recorded in an overlaid state.
The image forming apparatus of this kind, for example, has four photoreceptors, and forms the color image on the medium to be recorded by sticking toner of yellow, magenta, cyan, and black on each photoreceptor, transferring the toner of different colors carried by the photoreceptors to a medium to be recorded in an overlaid state.
However, when the position (referred to as a scanning position hereafter) of the scanned and irradiated light beams on the photoreceptor is different between each photoreceptor because generation timing of the light beams is different between each light beam source in this kind of image forming apparatus, there is a possibility that the toner stuck on each photoreceptor is not overlaid on each other on the medium to be recorded at a desired positional relation, and so-called color slippage occurs. Therefore, it has been proposed that at least two pieces of plastic lenses out of the lenses respectively disposed on a light path from the light beam source to the photoreceptor are formed with the same cavity, thus reducing error of each light path (for example, see Japanese Patent Laid-Open No. 2000-187173).